Sketch, on the same diagram, the graphs of and .
(You are not required to label any axial intercepts and stationary points.)
Solve exactly the inequality .
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Worked solution
2(i)
1. Determine the shape and vertex of $y = |2x + 3|$.
The graph of is a V-shaped curve opening upwards.
Its vertex (minimum point) occurs where the expression inside the modulus is zero:
Thus, the vertex is at .
2. Determine the shape and vertex of $y = -2x^2 - 8x - 3$.
The graph of is a parabola opening downwards (since the coefficient of is , which is negative).
The -coordinate of its maximum point is given by :
The corresponding -coordinate is:
Thus, the vertex of the parabola is at .
3. Determine the points of intersection to establish relative positions.
Set the equations equal to find the intersections:
Case 1 ():
Since , we accept .
Case 2 ():
Since , we accept .
The graphs intersect at two distinct points: and .
4. Sketch both graphs on the same axes.
Draw the coordinate axes.
- Sketch the V-shaped graph of touching the negative -axis.
- Sketch the inverted parabola with its maximum point to the left of the V-shape's vertex.
- Ensure the parabola crosses the V-shaped graph at exactly two points.
(As per the instructions, no labels for axial intercepts or stationary points are required.)
[A properly drawn sketch on Cartesian axes showing a V-shaped graph opening upwards with its vertex on the negative -axis, and an inverted parabola with its vertex in the second quadrant. The parabola must intersect the V-shaped graph at exactly two points.]
2(ii)
1. Find the intersection points by considering the positive case of the modulus.
To find where the graphs intersect, we solve .
For (i.e., ):
Using the quadratic formula:
Since , we reject (which is ), leaving .
2. Find the intersection points by considering the negative case of the modulus.
For (i.e., ):
Since , we reject , leaving .
3. Use the graphical representation to determine the final solution intervals.
The inequality requires the graph of to be above the graph of .
Referring to the sketch from part (i), the V-shaped modulus graph opens upwards, and the quadratic graph is an inverted parabola. The V-shape lies strictly above the parabola for -values outside the interval bounded by the intersection points.
Therefore, the solution to the inequality is:
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